This invention relates generally to double-hung window assemblies with at least one sash that slides vertically in the window frame and that also tilts relative to the frame about a horizontal axis. More particularly, the invention relates to a device for locking the horizontal pivot axis of the sash in a fixed vertical position during tilting to prevent undesirable upward movement caused by contraction of a counterbalance spring or the like.
In many modern window assemblies, the sash are slidable in combination weatherseal guides or jamb liners that are coextensive with the jambs at opposite sides of the window frame. The jamb liners or guides establish a weatherseal at the edge faces of the window sash, and at the same time provide for free guided vertical movement of the sash. The sash are usually counterbalanced by helical springs attached at their upper ends to the tops of the guides and at their lower ends to slides, which are in turn connected near the bottom of the sash. The sash are provided with pivot means connected to the slides so that they may be tilted inwardly about their lower ends to facilitate washing, for example.
This type of mounting is also adapted to permit removal and replacement of the sash for cleaning, painting and other purposes. The yieldably backed jamb liners permit sufficient lateral movement of the sash to free the end faces from the sashways or guide channels to disconnect the sash from the balance springs. However, when the sash are tilted away from the jamb liners, the sliding friction is substantially reduced, so that the tension or upward force provided by the counterbalance springs exceeds substantially the weight and friction force resisting movement. As a result, the springs tend to fly back and jerk the slides or sash connections violently upward.
Where the slides are provided with a locking means to prevent snap-back, the system used usually includes gripping devices that are intended to set and grip the jamb liners automatically in response to the force of the balance springs when the sash are tilted outwardly or removed. The gripping devices, however, when operated over a long period of time, can cause serious damage to the jamb liners. Typical devices in the prior art used to accomplish this purpose are shown in the following U.S. Pat. Nos.: 2,006,745, 2,989,773 3,135,014, 3,464,160, 4,644,691.
The clutching or braking means shown in these patents generally use sliding members that dig into the walls of the channels housing the springs, with the result that the inner walls soon become so abraded that it is difficult for the sash and slides to travel freely in the channels during the lifting and lowering of the sash. Other prior art devices use rods on the interior of the channel housing with wedging devices slidable on the rods and impinging against the rods to lock the ends of the springs in place. These devices eventually become inoperative because the rods become damaged and the slidable members become struck on the rods and prevent proper functioning of the window balance system.
The apparatus of the present invention resolves the difficulties described above and affords other features and advantages heretofore not obtainable.